Core construction



23, 1958 E J SCHAEFER 2,849,695

cons cous'mucnou filed Nov. 12, 1954 IN V EN TOR.

FauJQrdJSC/mefex Hitti e-i i; tare This invention relates to novel means for holding together a stack of sheet-like laminations and more particularly to a novel core construction such as used in the stator of a dynamoelectric machine or other electrical equipment.

In electrical equipment utilizing laminated cores, the most common means for securing the-"-'laminations to gether is by means of rivets, welds, or the like. ever, such constructions have well known disadvantages such as relatively high eddy current losses and disturbance of the insulating films covering the individual laminations. To overcome such objections, it has also been proposed heretofore to secure the stacked laminations together by. means of a key strip arrangement. For example, in Korski Patent No. 2,610,225, the stack of laminations is provided with a groove extending across the edges of the respective laminations, and an elongated key in the form of an outwardly bulged metal strip is fitted in the groove and then completely flattened so that the side edges of the strip are forced into engage- ,ment with the side walls of the groove to hold the laminations together without the necessity of rivets, welds, or the like.

Although the aforementioned keyed core construction is an improvement over the other methods heretofore employed, nevertheless, I have found that certain limitations are encountered with a transversely curved key strip in which the chord of the transversely curved portion is substantially the same as the width of the groove in the stack. As described in the Korski patent, a key strip of this character is flattened completely when installed in the groove of the laminated stack and it is apparent therefore that the resilience of the strip necessary to maintain lateral pressure against the sides of the groove must depend entirely on the inherent compressive resiliency of the metal from which the strip is formed. Consequently, with such a structure, there is little effective control over the resiliency of the key. Moreover from a practical manufacturing viewpoint, there may be slight variations in different instances in the width of the groove and the width of the key strip with the result that there may be insufficient transverse resilience and compression of the completely flattened key strip to hold it firmly in place in the groove.

Althoughit might be supposed that such difliculties could be cured by using a somewhat wider curved key strip and only partially flattening the strip, I have found that it is diflicult to obtain sufficient effective transverse or lateral pressure to hold the partially flattened key in place unless a relatively narrow and relatively thick key Howis used. However, a narrow thick key is also objectionable since it is desirable to make the key strip relatively wide compared to its thickness in order to impart lateral stiffness to the assembled core and thereby obtain maximum lateral rigidity without the necessity of a deep groove and a thick key which would impair the magnetic or electrical qualities of the core construction.

Accordingly, a primary object of the present invention is to provide an improved core construction utilizing novel key means for retaining the laminations of the core in stacked relation.

A further object of the invention is to provide novel means for providing a high degree of control over the resiliency of the key strip in a keyed core construction for a stator or the like.

Another object of the invention is to provide a novel keyed core construction which permits a desirable control of transverse resilience in the key without undue restrictions on the total width of the key.

Still another object of the invention is to provide a novel keyed core construction wherein the bent-over ends of the key strip have enhanced rigidity and resistance to outward flaring as compared with the keyed core constructions heretofore known.

An additional object of the invention is to provide a novel key strip element for use in a keyed core construction of the type described.

Other objects and advantages of the invention will become apparent from the subsequent detailed description taken in conjunction with the accompanying drawing, wherein Fig. 1 is a fragmentary end view of a stator core embodying the principles of the present invention;

Fig. 2 is a fragmentary side elevational view of the stator core shown in Fig. 1;

Fig. 3 is a perspective view showing one specific embodiment of a key strip as employed in the stator core construction shown in Figs. 1 and 2;

Fig. 4 is an enlarged fragmentary end view of the stator core showing the key in cross section as disposed in a groove prior to its being pressed into holding engagement with the laminations;

Fig. 5 is a view similar to Fig. 4 but showing the key after it has been pressed into holding engagement with the laminations;

Fig. 6 is an enlarged fragmentary side elevational view showing in a somewhat exaggerated manner the relation of the installed key to the stacked laminations;

Fig. 7 is an enlarged fragmentary end view of the stator core showing the manner in which the key strip is bentover at the ends of the core;

Fig. 8 is a fragmentary cross-sectional view through the stack as seen along the lines 88 of Fig. 7; and

Fig. 9 is a view similar to Fig. 5 but showing a modified groove construction.

By way of illustration, the invention is shown herein and will be described in connection with the stator core of a dynamoelectric machine such as a motor. be understood, however, that the same principles may be applied to other electrical equipment such as the rotors of dynamoelectric machines, transformer cores, and the like.

Referring to the drawing, the stator core of a motor is indicated generally at 11 and comprises a plurality of sheet-like laminations 12 which are superimposed in face- It is to.

to-face relationtofqtm an aligned stack in the usual manner. As is well known, such laminations may comprise shcet steel punchings the inner peripheries of which are formed with a plurality of circumferentiztlly arranged slots 13 for receiving the usual windings (not shown). in addition, the faces of the laminations 12 are normally covered with a suitable varnish, oxide, or scale so as to form an insulating barrier between adjacent laminations.

The laminations 12 also have punched-out slots at their outer peripheries which are aligned when the laminations are stacked together to provide a plurality of circumferentially spaced shallow grooves 14 extending axially with respect to the core and across the outer edge portions of the stacked laminations. In the embodiment of the invention illustrated in Figs. 4 and 5, each of these grooves 14' has asubstantially flat base or bottom wall 16 with upstanding substantially perpendicular side walls 17. Of course, the location of the grooves 14 circumferentially of the stator core may be arranged so as to cause the least interference with the electrical characteristics of the device.

For holding the laminations 12 together in stacked relation, an elongated key strip 18 (Fig. 3) is installed in each of the grooves 14 in the manner hereinafter described. The key strip 18 prior to installation thereof comprises an elongated strip of metal, such as a half-hard cold rolled steel or other relatively soft tempered steel, having at least one transversely curved or arched portion the chord of which is substantially less than the width of the groove 14. Preferably, a plurality of such arched portions are provided so that in transverse cross-section the strip has a generally corrugated construction with the arched portions extending longitudinally of the strip. In the embodiment herein illustrated, the strip 18 has a substantially flat central portion 19 extending the full length of the strip and on opposite sides thereof a pair of outwardly bulged or transversely curved edge portions 21'.

To install the keys 18in the grooves 14, the stacked laminations 12 are held together by some auxiliary means such as clamps or the like, and the key 18 with its initial fully curved portions 21 is inserted in the appropriate groove as shown in Fig. 4. It will, of course, be understood that the initial total width of the key 18 is slightly less than the width of the groove 14 so as to permit this initial insertion. External pressure is then applied against the key so as to effect incomplete or partial flattening of the curved portions 21 to the position shown in Fig. 5. Obviously, this limited flattening action is suflicient to cause the edges of the key strip 18 to move laterally and engage the side walls 17 of the groove with a tight frictional pressure so as to hold the stacked laminations together.

When the peripheral slots are punched in the laminations 12 for forming the grooves 14, the effect of the punch as it enters the metal is to compress the edge of the metal at that point and as the punch breaks through the metal on the opposite side it tends to leave a sharp edge. Consequently, as shown on a somewhat exaggerated scale in Fig. 6, when the punched laminations are stacked or fitted together all in the same relation With respect to the direction of punching, a plurality of small wedge-shaped openings or interstices 22 are provided between the adjacent laminations around the boundaries of the groove 14. When the key strip 18 is in the partially flattened Fig. condition, the high degree of transverse or lateral pressure causes the relatively soft metal of the key strip 18 to flow into the interstices 22, as indicated at 23. In addition to the strong lateral pressure between the side edges of the key strip 18 and the side walls 17 of the groove, this wedging action or interstitial flow of the metal greatly augments the holding power of the key and tends to hold each lamination individually so that the overall rigidity of the structure is improved.

The important features of my invention are: (1) the restricted chordal dimension of the arched portion of the 4 key strip relative to the width of the groove so that the width of the arch is controlled independently of the total width of the strip, and (2) the fact that the arched portions 21 of the key strip 18 are only partially flattened during installation of the key so that the partially flattened curved portions are still spaced slightly above the base 16 spending side edges of the groove. I have found that by utilizing at least one and preferably a pair of transversely curved portions each of which has a chordal dimension substantially less than the width of the groove and each of which is only partially flattened during installation of the key strip, I can obtain excellent control over the extent of transverse resilience in the installed key without unnecessarily restricting the width of the key. As previously pointed out, such control over transverse resilience by partial flattening is not possible with a key strip having only a single transverse curvature extending across the entire width of the strip except by unduly restricting the width and increasing the thickness of the key strip. With the key strip construction of the present invention, I can utilize a relatively wide key so as to have all the advantages of lateral stiffness and rigidity without the necessity of employing a deep groove and a thick key which would seriously impair the magnetic or electrical properties of the core construction. Moreover, by controlling the degree of partial flattening of the strip, the construction readily compensates for minor variations in key strip width and also in the width of the groove.

After the key strip has been installed in the groove by partial flattening as described above, the opposite end portions of the strip which remain substantially unflattened and which project beyond the ends of the stator core are bent-over at right angles, as at 26, into axially compressive relation with the opposite axial ends of the stack. I have found that the key strip construction of the present invention imparts an additional advantage in that the plurality of curved portions 21 function as strenghtening or stiffening ribs thereby eliminating any tendency of the strip to develop waves upon flattening. This stiffening effect is particularly important at the end portions 26 of the key strip and the sharp bends thereof so that the bent end portions have very substantial holding power. Consequently, there is little or no tendency for the bent-over end portions 26 to spring out or disengage themselves from the ends of the stack which is a difficulty frequently encountered with the key strips heretofore suggested in the art. Moreover, there is a slight degree of lateral spreading or flaring, as at 27 in Fig. 7, when the end portions 26 are compressed against the ends of the stack which further contributes to the retention of the end laminations in stacked relation.

In Fig. 9, the invention is illustrated in connection with a modified groove 28 wherein the base or bottom wall of the groove has a generally concave or deprssed configuration, as indicated at 29. This particular groove shape has the advantage that, once the key strip 18 is installed and partially flattened under pressure, the central portion 19 thereof is depressed into contact with the lowermost portion of the concave bottom 28 of the groove so that-the central portion of the strip 18 is in over center depressed relation with respect to the side edges of the strip. It will be apparent that once the key strip 18 is thus sprung into the over'center position shown in Fig. 9, it will have substantially higher stability and considerably greater resistance to inadvertent detachment from the groove. At the same time, the partially flattened curved portions 21 provide the desired controlled transverse resilience for insuring sustained lateral pressure of the key strip against the sides of the groove.

Although the invention has been described with particular reference to certain specific structural embodiments thereof, it is to be understood that various modifications and equivalent structures may be resorted to without departing from the scope of the invention as defined in the appended claims.

I claim:

1. In combination. a stack of laminations superimposed in face-to-face relation, said stack having a groove extending across the edges of the respective laminations, and a key fitted in said groove for holding the laminations in stacked relation, said key comprising an elongated strip having a longitudinally extending fiat portion engaging the base of said groove and a longitudinally extending and transversely arched portion with its chord substantially less than the width of said groove, said arched portion being only partially flattened from an initial unflattened condition and the radius of curvature of said par-. tially flattened arched portion being substantially greater than the radius of curvature of the arched portion in its initial unflattened condition whereby the longitudinal edges of the strip have tight frictional engagement with the corresponding sides of said groove for securing the laminations together and whereby the partially flattened arched portion is still arched slightly from the base of said groove, the residual curvature of said partially flattened arched portion providing sufiicient transverse resilience in the strip to insure said tight frictional engagement.

2. In combination, a stack of laminations superimposed in face-to-face relation, said stack having a groove extending across the edges of the respective laminations, and a key fitted in said groove for holding the laminations in stacked relation, said key comprising an elongated strip having a longitudinally extending flat portion engaging the base of said groove and a plurality of longitudinally extending and transversely arched portions with chordal dimensions substantially less than the width of said groove, said arched portions being only partially flattened from an initial fully arched condition and the radius of curvature of said partially flattened arched portions being substantially greater than the radius of curvature of the arched portions in their initial unflattened condition whereby the longitudinal edges of the strip have a sustained tight frictional engagement with the corresponding sides of said groove for securing the laminations together, said partially flattened arched portions having sufficient residual curvature to provide transverse resilience in said strip whereby to insure said sustained tight frictional engagement without the use of a key strip of restricted width or excessive thickness.

3. In combination, a stack of laminations super-imposed in face-to-face relation, said stack having a groove extending across the edges of the respective laminations, and a key fitted in said groove for holding the laminations in stacked relation, said key comprising an elongated strip having a substantially flat longitudinally extending central portion engaging the base of said groove and a pair of outwardly bulged transversely curved portions extending longitudinally along the side edges of the strip on opposite sides of said central portion, said transversely curved portions being only partially flattened from an initial fully curved condition at the time of insertion of the strip in the groove and the radius of curvature of said partially flattened curved portions being substantially greater than the radius of curvature of said curved portions in their initially fully curved condition whereby the side edges of the strip are forced into sustained tight frictional engagement with the corresponding sides of said groove but the partially flattened portions are still arched slightly from the base of the groove, and said partially flattened portions having sulficient residual curvature to provide transverse resilience in said strip whereby to insure said sustained tight frictional engagement for securing the laminations together.

4. In combination, a stack of laminations superimposed in face-to-face relation and having a groove extending across the edges of the respective laminations, said groove having oppositely disposed side walls and a generally concave base, and a key fitted in said groove for holding the laminations in stacked relation, said key comprising an elongated strip having a substantially fiat longitudinally extending central portion and a pair of outwardly bulged transversely curved portions extending longitudinally along the side edges of the strip on opposite sides of said central portion, each of said curved portions being only partially flattened from an initial fully curved condition at the time of insertion of the strip in the groove whereby the side edges of the strip are forced into sustained tight frictional engagement with the side walls of the g oove for securing the laminations together but the partially flattened portions are still arched slightly from the base of the groove, said partially flattened portions having sufficient residual curvature to provide transverse resilience in said strip whereby to insure said sustained tight frictional engagement, and the central portion of said strip being depressed inwardly against the concave base of the groove in over center relation with respect to the side edges of the strip whereby to resist detachment of the strip from the groove.

5. The structure of claim 1 further characterized in that interstices are defined between adjacent laminations in said stack at the walls of said groove and the material of said strip is forced into said interstices whereby to hold the laminations individually and thereby increase the keying elfect of the strip.

6. The structure of claim 5 further characterized in that the end portions of said strip project beyond the ends of the stack and retain substantial curvature, said end portions being bent over into axially compressing engagement with the ends of the stack with the arched portions thereof imparting increased rigidity to the bent over end portions whereby to stiffen and retain the same in contact with the ends of the stack.

7. In combination, a stack of laminations superimposed in face-to-face relation, said stack having a groove extending across the edges of the respective laminations, and an elongated key strip fitted in said groove with the longitudinal side edges of the strip in tight frictional engagement with the corresponding sides of said groove for securing the laminations together, the end portions of said strip projecting beyond the ends of the stack and being bent over into axially compressing engagement with the ends of the stack, and said end portions including the bends therein having transverse curvature for imparting increased rigidity thereto whereby to stiffen and retain the same in contact with the ends of the stack.

8. The structure of claim 1 further characterized in that the end portions of said strip project beyond the ends of the stack and retain substantial curvature, said end portions being bent over into axially compressing engagement with the ends of the stack with the arched portions thereof imparting increased rigidity to the bent over end portions whereby to stiffen and retain the same in contact with the ends of the stack.

9. A key for holding together a plurality of stacked laminations, said key comprising an enlongated strip having at least one transversely arched portion extending the,

length of the strip with its chord substantially less than i the total width of the strip and the side edges of the strip laminations. said key comprisingan elongated strip hav- 7 ing a substantially flat central portion and a pair of outwardly bulged transversely curved portions extending along the side edges of the strip on opposite sides of said central portionsuid curved portions being adapted to be partially flattened for forcing the side edges of the strip laterally into sustained resilient frictional engagement with the sides of a groove in the stack of laminations, the side edges of the strip being substantially perpendicular to a tangent to the cross-sectional curvature at the edges and at an angle to a line extending transversely across the strip to provide a sharp edge spaced outwardly from the bottom of the groovea 8 t References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Kimble, abstract Ser. No. 703,322, published July 12, 1949. 

